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The transferability of the valence ionization intensities of chemical functional groups is investigated with three common laboratory ionization sources (Ne Iα, 16.7 eV; He Iα, 21.2 eV; and He IIα, 40.8 eV) for a series of molecules. Each molecule contains two different functional groups that are well separated electronically and spatially by an alkane chain linker. The optimum length of the alkane chain between the functional groups is investigated. In this initial study, the functional groups are RCl, RBr, RSH, and RFc, where R is an alkane chain and Fc is ferrocene with an alkane chain bonded to one cyclopentadienyl ring. An additional feature of this study is that each functional group contains a molecular orbital with nearly pure atomic character, allowing comparison to theoretical atomic ionization cross-section ratios. In general, the observed photoelectron intensity changes are more gradual than those predicted by either theoretical atomic photoionization cross sections or by a complete Gelius analysis based on molecular orbital compositions obtained from electronic structure calculations. Experimentally, there is a high degree of transferability of the relative ionization intensities of the chemical functional groups between the molecules of this set. These results indicate that an empirical library of the relative ionization cross sections of chemical functional groups as a function of photon energy will be a useful aid to the study of more complex molecules and will provide an experimental foundation for further theoretical studies of molecular photoelectron cross sections.

He I photoelectron spectra of phenanthrene (1), 1,10-phenanthroline (2), phenazine (3), dibenzo[a,c]anthracene (4), dibenzo[a,c]phenazine (5), and dipyrido[3,2-a;2‘3‘-c]phenazine (6) have been obtained. Assignment of the π ionization states was aided by electronic structure calculations:  the first ionization state of 1, ²B1(π1), is observed at 7.888 ± 0.002 eV, ²B2(π1) of 2 is at 8.342 ± 0.002 eV, and ²B1g(π1) of 3 is at 8.314 ± 0.002 eV. Spectra of 4−6 are reported for the first time:  ²A2(π1) of 4 is at 7.376 ± 0.002 eV, and both 5 (7.983 ± 0.002 eV) and 6 (8.289 ± 0.002 eV) exhibit quasi-degenerate first and second ionization states. Quantum-mechanical reorganization energies, λ^QM, were extracted from analyses of vibrational structure:  values are 149 ± 5 (1), 167 ± 5 (2), 68 ± 2 (3), and 92 ± 4 (4) meV. Low-frequency modes were treated semiclassically:  values of λ^SC are estimated to be 21 ± 1 (1), 13 ± 1 (2), 22 ± 1 (3), 66 ± 1 (4), 27 ± 9 (5), and 16 ± 1 (6) meV. Reorganization energies (λ = λ^QM + λ^SC) of isolated molecules are 170 ± 5 (1), 180 ± 5 (2), 90 ± 2 (3), and 158 ± 4 (4) meV. Density functional calculations (B3LYP/6-311G++(d,p)) give λ values that are on average 63 meV lower than experimentally derived energies.

We investigate by means of gas-phase ultraviolet photoelectron spectroscopy complemented by quantum-chemical calculations how the frontier levels of the 4,4‘-bis(N-m-7tolyl-N-phenylamino)biphenyl (TPD) molecule are affected upon substitution of the terminal aryl rings with methoxy groups or fluorine atoms. These results provide strategies to modulate energy barriers at metal/organic or organic/organic interfaces involving TPD and its derivatives; it is shown that the change in the energy of the HOMO level of TPD upon derivatization is strongly affected by inductive effects taking place in the σ skeleton.

Conformational analysis of 1,4,7-trithiacyclononane, [9]aneS3, in the gas phase was done using three techniques:  ab initio molecular orbital calculations at the HF and MP2 levels as well as microwave and photoelectron spectroscopies. The photoelectron spectroscopic data show evidence for at least two conformations with different ionization energies. Using the calculated photoelectron spectra, the observed sulfur 3p ionization peaks can be assigned to C1 and C2 conformations. Forty of the observed microwave transitions can be assigned to a C1 symmetry, asymmetric top, rigid rotor spectrum with rotational constants A = 1155.651(3) MHz, B = 998.442(3) MHz, and C = 629.426(2) MHz. Additional microwave lines are believed to be due to a nonrigid C2 symmetry conformation. No significant populations of conformers of higher symmetry are found.